Problem with a Keston Celsius C25 boiler

[Bronzie]

Hi All

I work for a small family housebuilders. I am therefore not a plumber, but am conversant with most installations and boiler types (speak slowly and clearly to me and I should be fine ;-) ). We recently built a couple of new houses near Hemel Hempstead and specified Keston C25 boilers, mainly because of their flexibility with regard to flueing.

Both properties were only moved into in Jun'06, although the boilers were actually installed in Sep'05 (the houses stood empty over Winter with heat on low). The boilers have therefore only been in use for a relatively short time with little call for full heating output.

Yesterday I got a call from one of the homeowners saying they had no heat. Not being able to pin the fault down, I paid them a visit and found water dripping out of the casing. On taking the cover off the boiler, this is what I saw:

exhaust tube has completely disintegrated, allowing exhaust gases and condensation into the casing. Not sure why the boiler stopped firing (it was still running although only for a few seconds before closing down) but I'm glad it did.

Keston Service were not very helpful saying they could not visit until Friday. This left me with a very irate and cold customer. Being relatively easy to replace, I set about finding a replacement (no easy task).

I finally managed to get another tube and replaced it and left the boiler running OK but I'm now very concerned that we have installed a pair of crap boilers (having read the other Keston threads only reinforces this concern). I have e-mailed Keston Technical for comment but so far no reply (and understand they are in the process of being taken over, so maybe indicates no reply any time soon).

Any ideas what has gone wrong to cause this fault? I suspect the boiler has run very hot, melting the tube, but it is supposed to have a flue overheat sensor to stop the boiler running in this scenario. Has anyone else come across this sort of problem?

Cheers Bronzie

[Andrew Gabriel]

Keston seem to have changed the design of the exhaust tube now to something more like a thick rubber hose. Mine (which is about 4 years old) has the type in your picture, but it hasn't disintegrated. However, I've only run my Keston at about 45C flow temperature (it does heating only, not the hot water). I have got a spare exhaust tube ready though, given what happens to these older ones.

HRPC (part of Plumb Center) stock them. You should get a different design now (solid, not consetina).

If hot fumes are pumped back into the casing, there's a thermal fuse which trips (mounted on the transformer terminals). If you didn't end up replacing that (it's not resettable), then I suspect the failure did not result from very hot exhaust, but just a materials failure of the exhaust pipe being unsuitable for what it's being used for. This would also be backed up by Keston's change of the design.

After reassembling any part of the flue, I would do a very good check for water soundness, as any leak in it will quickly do very serious damage to the boiler (it will corrode through the casing, which would be rather non-trivial to repair for the rear part at least). I did this by setting the garden hose to a tiny trickle, and pushing it in the end of the exhaust flue outside. Check the water is coming out through the condensate drain and leave it running for 15 minutes or so. Check all the flue pipework inside and outside the boiler for any sign of water leaks. Obviously, do this with the boiler power disconnected, in case you do get any leaks. Leaks at the top spigott can run along the top of the casing and onto the mains transformer at the other side.

The other things which people have reported going wrong with these boilers on a few occasions are: Ignition electrode softens and droops away from burner, making ignition progressively more difficult until it eventually fails. The electrode can be easily removed, but the ignition wires must be heated red hot to be bent back and the gap reset or you'll snap them -- they go very crystaline/brittle. Combustion chamber condensate drain hole gets blocked, and the boiler starts making girgling noises as condensate collects, until it finally blocks the flue outlet and goes out.

[Doctor Drivel]

Bronzie,

The burner may be incorrectly set and running too hot, hence the disintegration of the rubber tube. This can only be done with an analyser. Get Keston to check this out and claim back the cost of the part - you fitted it because their service was poor and you were responsible and would not leave a customer.

The fluing is very flexible. What did you do with the flue?

Despite the problem you have had they are a good boiler with many on this group having them. The initial problems have tended to have been ironed out of the boiler.

[Tony Bryer]

The originals were a blue polythene-type material. We had the same trouble as the OP on one of our church boilers and replaced it with the new pattern heavy black hose and Keston replaced the other for free as part of their fixed price summer service a year or so later. The design is poor though - I cannot see why they could not have a rigid pipe (with a socket-up O-ring joint for expansion if necessary).

My experience of HRPC 'stocking' Keston parts has been less than satisfactory and Keston's MD got a letter from me to that effect.

I've got oversight of three Celsiuses - two at the church, one at my mum's. The latter has never had any ignition problems, but did fail last year on the blocked condensate outlet (which I failed to pick up). Meanwhile the two at the church have had repeated ignition problems - we had another PCB changed for free during this summer's service. The electrode design has been changed, but the new pattern is not immune to movement. You understand electronics: I wonder if when the electrodes move to an extent where there is no spark, the PCB is damaged by all that HT having nowhere to go?

Our church two were very early models, and I do give Keston marks for learning from site experience and improving the design of various parts. It's just that they need to do a little more yet.

[Bronzie]

Thanks for the advice so far. I have spoken to Keston Service again today and left the planned visit booked with a note that I have replaced the damaged part but would still like them to check the boiler operation.

The thermal fuse was OK as the boiler ran fine when I re-started it. Checked flue temperature at outlet which didn't go above 51=B0C while I was there.

I didn't use any sealant when I replaced the flue...........until I saw condensate dripping out and twigged that the poor design of this fitting (should be a male spigot on the end of the exhaust hose so it fits INSIDE the exhaust outlet!) means that sealant is required. I smeared a load of Fernox LSX inside the end of the tube and re-fitted without any apparent leak. But difficult to start running hoses into customers boilers though - not sure they would be too keen for me to start doing this!

I'll see what Keston have to say tomorrow. Still no spare part turned up from them yet.

I also tried HRPC and have ordered a spare with them just to keep one in hand, but not available until Monday unless I wanted a trip to a branch in Scotland to collect one!

I'll keep you posted on developments.

[Bronzie]

Got the replacement hose from Keston this afternoon - here are the old and new side by side:

the replacement that I fitted was the same type as I removed, so possibly the problem could re-occur.

I have left the service visit from Keston booked, and fingers crossed, their engineer will swap the one I fitted for the new type and check the boiler operation at the same time.

Obviously then, this problem is known to Keston, otherwise they wouldn't have changed the design.

[Andrew Gabriel]

I mail ordered. The order has arrived in a couple of different packages from different Plumb Centers (sick), as none had all the parts in stock (I ordered a number of replacement gaskets and an ignitor too). The ignitor is not an HRPC stock item, so I'm still waiting for that. However, the one I bent into a usable shape (after having snapped the end off it trying to bend it cold) is working brilliantly, lighting the burner first time every time.

I've never pulled the PCB out to look at it's design. I would have expected the EHT lead not to go into the PCB board, but come off the top of the transformer. The transformer might break down internally if the spark gap is too big, but it might have a built in spark electrode to protect it from this.

In my case, the drooping electrodes had not significantly opened up the gap, but moved them too far from the burner.

[Andrew Gabriel]

The flue gas is 5C hotter than the return water temperature. It's at the wrong side of the heat exchanger to be much affected by the burner. The heat exchanger would have had to be without water too for hot flue gasses to leave the combustion chamber, and that would trip the over temperature sensor.

This particular test could be done by checking the gas flow rate at the meter, as described in the installation manual. (You can't set the mixture without a flue gas analyser though.)

[Tony Bryer]

From my letter to Keston's MD, Nick Stevenson, last March following my 3 week wait for a condensate trap ordered through Parts Center

"... As your website refers parts enquiries to trade outlets I would suggest that you and they really need to get your act together to ensure the timely delivery of spare parts. ...".

If nothing else is kept in stock surely igniters and the burner gasket should be on the shelf of every branch, and probably flue hoses. Is it so hard for firms like Keston to realise that if you want to compete with the big boys making life hard for those who will recommend, install and fix your products is not the way to go.

[Bronzie]

Heard from my customer now to confirm that Keston engineer arrived at planned time and did indeed change the exhaust tube to the new design.

Keeping fingers crossed that this is the last problem I encounter with any of the 4 Kestons we have now installed!

Thanks again for the help & advice

Bronzie